Contemporary hard disk drives include an actuator assembly pivoting through an actuator pivot to position one or more read-write heads, embedded in sliders, each over a rotating disk surface. The data stored on the rotating disk surface is typically arranged in concentric tracks. To access the data of a track, a servo controller first positions the read-write head by electrically stimulating the voice coil motor, which couples through the voice coil and an actuator arm to move a head gimbal assembly in positioning the slider close to the track.
When the slider is positioned close to the rotating disk surface, an air bearing forms, supporting the read write head at a flying height near the disk surface. The flying height is very small, often less than ten nanometers. This is an inherently dangerous situation. The slider can easily get too close or too far away from the rotating disk surface. These situations degrade the ability of the read-write head to access the data on rotating disk surface. Worse yet, in the case of collisions, the data being stored on the rotating disk surface and/or the read-write head may be damaged.
Methods and apparatus are needed to estimate the flying height of the read-write head near the rotating disk surface. Methods and apparatus are further needed to adjust the flying height based upon the estimated flying height.